Garden Detective: How to kill sassafras roots once and for all

DEAR JESSICA: I can't get rid of hundreds of sassafras saplings. I love the smell of root beer when I mow them, but within a few days the leaves grow back. I tried Tenacity and a few other weed killers but nothing works. Using a weed tool is extremely arduous. They can be very deep. Even when I dig them up, they grow back. This root-sucker type tree doesn't seem to care about photosynthesis. It's getting all of its nutrients from the soil. Since the momma tree was taken down a couple of years ago, will these saplings eventually die off, if not, how can I kill this stuff without destroying my lawn? — Tom Sundberg, East Northport

DEAR TOM: What you’re witnessing is your cut-down tree trying to save its lineage. When many types of trees are dying or cut down, as yours has been, their root systems make a last-ditch effort to propagate heirs. In a forest, this ensures that nature will persevere. In your backyard, it ensures you’ll get frustrated and write to the Garden Detective.

There are growth-regulating products containing Napthaleneacetate that are quite effective at stopping suckers from sprouting from live trees. They also could have been used to treat the freshly cut stump when you removed the tree, and the chemical would have been transported from the still-living stump to the root system, eventually killing it. In this case, timing is everything; the horse is out of the stable now, so trying this today would be Sisyphean — you’d see improvement for a while as suckers are killed, but new ones would replace them, and you’d have to reapply periodically, possibly forever.

Instead, you’ll need to eliminate the source of those suckers by completely removing or killing the remaining underground roots. Digging them up would do the trick, but isn’t practical. The roots are likely deep and big, and chopping them would just spur new suckers. Instead, you’ll have to use the tree’s own food-delivery system against it.

You seem to have a good knowledge of photosynthesis, but the product you’re using is likely killing the leaves before they can do any damage. If you kill the leaves quickly, all you’ve done is kill the leaves. And those roots have a lot of stored energy so they can make more. The goal is to keep the leaves alive long enough to deliver the goods.

Let’s take a moment to discuss how plants, including trees, nourish themselves. Simply put, leaves absorb sunlight and use it (along with gasses and water) to photosynthesize, which means to produce food for itself. This food (glucose) is then translocated from the leaves, through the plant, to the roots, which store it as energy to use later.

You need to trick the plant into sending a chemical (instead of food) to its roots, and you can accomplish this by spraying the leaves of your suckers with a systemic herbicide containing triclopyr, such as Bayer Brush Killer Plus. If you follow the directions carefully (don’t apply more than called for) the product will be absorbed into the leaves and travel through the plant to its roots, where it will prove fatal over time. You may need to repeat this, but it should do the trick. The product is considered safe for most grasses, except stoloniferous types like zoysia.

DEAR JESSICA: I emptied my patio pots, and there were these bugs throughout the soil. I picked them out and put them in hot soapy water to kill them before adding the soil to my compost pile. What are these things? I always use MiracleGro potting soil, and the pots are elevated from the patio by discs. I've never seen them. There were 20 to 30 per pot. Yuck! — Laura Devito, East Quogue

DEAR LAURA: Those are grubs! Commonly found in lawns, where they live beneath the soil and eat turf roots, the off-white, brown-headed beetle larvae that look like curled-up shrimp sometimes show up in planters. In small numbers, they don't pose much of a risk, but when populations rise to more than 10 grubs per square foot, control measures are recommended to prevent endangering plant health.

It's a good thing you disposed of the potting soil, but I would not have recommended adding it to your compost pile, which might not get hot enough to kill any eggs or larvae you might have missed. To avoid the risk of plants falling victim to grubs next year when exposed to the compost, screen it before spreading it around. (It's important to point out that grubs found in compost piles are often the larvae of a different kinds of scarab beetles, which are more likely to feed on decaying matter than roots. The larvae you found in your planter were Japanese beetle or June bug larvae, which do consume roots.)

Before reusing the pots, be sure to scrub their interiors with a brush and a solution of 90 percent water and 10 percent bleach, then rinse well and allow to dry.